1. Field of the Invention
The present invention relates to an axial-flow type fan having an air outlet blade structure. More particularly, the present invention relates to an axial-flow type fan having an end-cornered cutting blade structure proximate an air outlet of a fan housing, thereby reducing air-shearing noise in operation.
2. Description of the Related Art
Referring initially to FIG. 1, it illustrates a conventional fan housing structure having an air outlet connecting with an air inlet. The fan housing 10 forms an air-boosting inlet 11, an air channel 12 and an air outlet 13. A fan wheel (impeller) 20 is accommodated in the air channel 12, and consists of a hub 21 and a plurality of fan blades 22 arranged about a rotary axis of the hub 21. Each of the fan blades 22 has an air outlet corner 23. In operation, when the fan wheel 20 is rotated, the fan blades 22 drives air and the air outlet corner 23 may cause air turbulence on an inner circumference of the fan housing 10 that generates air noise. Hence, there is a need for a fan blade structure which can reduce air turbulence and air noise.
Referring to FIG. 2, it illustrates another conventional fan housing structure having an air outlet connecting with an air inlet. The construction of the conventional fan structure described above is disclosed in U.S. Pat. Nos. 4,734,015, 4,743,173, Re34,456, 4,806,081, 4,992,029, 5,028,216, 5,135,363 and 5,267,842 etc. The fan structure consists of a fan housing 10 and a fan wheel (so-called impeller) 20 accommodating therein. The construction of the fan housing 10 is shaped square including an air inlet side (so-called upstream side) and an air outlet side (so-called downstream side) disposed at its either side. The air inlet side forms an air-boosting inlet 11 while the air outlet side forming an air-expanding outlet 13′. An air channel 12 connects between the air-boosting inlet 11 and the air-expanding outlet 13′. The fan wheel 20 is accommodated in the air channel 12, and consists of a hub 21 and a plurality of fan blades 22 arranged about a rotary axis of the hub 21. The construction of the hub 21 is a barrel-shaped object having an outer circumference on which equi-spaced and titled the fan blades 22 each of which forms a flat vane. In operation, when the fan wheel 20 is rotated, the fan blades 22 drives air to suck into the fan housing 10 through the air-boosting inlet 11 that increases air pressure. Subsequently, airflow may pass through the air channel 12 and exhaust from the air-expanding outlet 13′ that steadies an exhausting airflow.
However, there exist several drawbacks of the axial-flow type fan in use. Each flat vane of the fan blade 22 has an outlet corner portion 23 at its endmost corner. The outlet corner portion 23 of the fan blade 22 is situated in the longitudinal section of the air-expanding outlet 13′ starting from the starting point A, as best shown in FIG. 2, and almost perpendicular to a surface of the air-expanding outlet 13′. When the fan blades 22 drive a mass of the exhausting air exhausting from the air-expanding outlet 13′, the air-expanding outlet 13′ guides and steadies the exhausting air for exhausting from the fan housing 10. In the longitudinal section of the air-expanding outlet 13′, the flat vane portion of the outlet corner portion 23 drives a transverse airflow in the air channel 12 that may generate air turbulence on the annular surface of the air-expanding outlet 13′ and cause air-shearing noise.
The present invention intends to provide an axial-flow type fan having an end-cornered cutting blade structure proximate an air outlet of a fan housing. When the fan is rotated, the end-cornered cutting blade structure is able to eliminate a transverse airflow in an air channel and thus to reduce air-shearing noise in such a way to mitigate and overcome the above problem.